The present invention relates to a method of winding an optical fiber on a reel suitable for storage and transportation of the optical fiber.
Conventionally, a technique has been keenly studied to increase transmission capacity in optical transmission using an optical fiber.
To increase transmission capacity in optical transmission, an optical fiber for optical transmission is required to be single-mode with the wavelength of use. This is because, when transmission through an optical fiber is performed in a plurality of modes, a mode dispersion inevitably occurs due to a difference in group velocity for each transmission mode, resulting in a deterioration of signal waveform.
In view of this, a single mode optical fiber (SMF) having a zero dispersion wavelength around the wavelength of 1300 nm was used. By this optical fiber, an optical transmission with transmission distance exceeding 100 km and transmission capacity of several hundreds of Mbps were realized. As shown, for example, in FIG. 6, this SMF had a refractive index distribution structure composed of a central region 61 serving as the core and a clad 62.
On the other hand, since the transmission loss of an optical fiber becomes minimum around the wavelength of 1550 nm, it was desirable to perform optical transmission using this wavelength band. Therefore, a dispersion-shifted optical fiber (DSF) having a dual shape refractive index distribution structure and the zero dispersion wavelength around the wavelength of 1550 nm was realized.
Further, in these days, wavelength division multiplexing optical transmission system (WDM system) is being very actively studied and developed as a technique for further increasing transmission capacity. Then, an optical fiber suitable for use in WDM optical transmission is being examined from various viewpoints.
When using an optical fiber in WDM system, it is required that there should be no zero dispersion wavelength in the operating wavelength band, from the view point of preventing four-wave mixing. Thus, a non-zero dispersion-shifted optical fiber (NZDSF) has been developed. The NZDSF little involves four-wave mixing, so that, at present, it is regarded as most suitable for WDM system, and it is being rapidly put into practical use.
Further, taking into account broadband WDM system, some NZDSFs have a large effective core sectional area (Aeff) in order to reduce non-linearity, and others have a reduced dispersion slope in order to decrease dispersion difference between wavelengths.
Specifically, the characteristics of a conventional DSF are, for example, as follows: Aeff, 50 xcexcm2; dispersion slope, 0.07 ps/nm2/km.
In contrast, an example of an NZDSF with an increased Aeff has the following characteristics: Aeff, 72 xcexcm2; dispersion slope, 0.11 ps/nm2/km. In this example, the emphasis is on the enlargement of Aeff.
An example of an NZDSF with a reduced dispersion slope has the following characteristics: Aeff, 55 xcexcm2; dispersion slope, 0.045 ps/nm2/km. In this example, the dispersion slope is reduced while maintaining an Aeff equal to or not smaller than that of the conventional DSF.
Some NZDSFs have characteristics other than those mentioned above. To achieve these characteristics, the refractive index distribution structure of NZDSFs tends to become more complicated than that of the conventional DSF.
Generally speaking, an optical fiber is shipped in a state, in which it is wound on a reel. A too-high winding tension when winding the optical fiber on the reel leads to an increase in transmission loss, whereas a too-low winding tension leads to loosen the winding on the reel due to vibration during transportation, and the like.
In particular, in the case of an NZDSF, the refractive index distribution structure is rather complicated as compared with that of a conventional DSF, in order to enlarge the Aeff and reduce the dispersion slope. Thus, the NZDSF is rather sensitive against bending and lateral pressure as compared with the conventional DSF.
For example, when wound at a bending diameter of 20 mm, the loss increase at a wavelength of 1550 nm is less than 1 dB/m in the conventional DSF, whereas it is approximately 5 dB/m in the optical fiber with reduced dispersion slope and approximately 20 dB/m in the optical fiber with enlarged Aeff.
Thus, it is important to optimize the winding condition of the optical fiber on a reel. For example, there is a method proposed as a method of winding a conventional DSF around a bobbin. In this method, the optimization of the winding condition is attempted by controlling the winding tension (0.1 N to 1 N) and the hardness of the barrel of the bobbin, in order to minimize an increase in transmission loss.
However, as stated in the above, the NZDSF is rather sensitive against bending and lateral pressure as compared with the conventional DSF. Thus, if the technique for a DSF is applied to the winding condition for the NZDSF, it would lead to an increase in transmission loss.
Further, to minimize the increase in transmission loss due to lateral pressure in an optical fiber, it is necessary to take into account not only the tension but also the winding diameter, winding pitch, and the like. Also from this viewpoint, the technique for winding DSF is to be regarded as incomplete.
Regarding DSFs including NZDSFs, it is known that minimizing the increase in bending loss is possible by shifting the cutoff wavelength to the longer wavelength side in order to enlarge the Aeff.
However, while the conventional technique proves convenient for an optical fiber used around 1550 nm wavelength, it does not allow single-mode transmission around the wavelength of 1300 nm, which means it is not suitable for optical transmission around the wavelength of 1300 nm.
Thus, at present, it is considered that an increase in bending loss is inevitable in an optical fiber suitable for use in WDM system and intended for single mode operation around the wavelength of 1300 nm. There is a great demand for a technique for winding such an optical fiber on a reel, without increasing transmission loss and loosening the winding.
The present invention is a method of winding an optical fiber on a reel, utilizing
the optical fiber having the following characteristics:
effective area Aeff is larger than 50 xcexcm2,
zero dispersion wavelength is outside a wavelength range of 1530 to 1565 nm,
absolute value of the dispersion value in the entire wavelength range of 1530 to 1565 nm is in a range of 2 to 14 ps/nm/km, and
bending loss at a wavelength of 1550 nm is in a range of 1 to 100 dB/m when wound at a diameter of 20 mm; and
the reel with a barrel diameter of not less than 100 mm and not more than 200 mm;
characterized by
winding the optical fiber on the reel with satisfying conditions of d less than p less than 2d and 0.004xe2x89xa6(2T/D)xe2x89xa60.007,
wherein d is a coating outer diameter of the optical fiber (mm), D is a barrel diameter of the reel (mm), T is a winding tension (N), and p is a winding pitch (mm).
In this specification, the terms are based on the definitions according to ITU-T G. 650 unless defined specifically.
Other and further features and advantages of the invention will appear more fully from the following description, with referring to the accompanying drawings.